Formation of brominated disinfection by-products and bromate in cobalt catalyzed peroxymonosulfate oxidation of phenol

•Br− can be activated by PMS both in the absence and presence of Co2+.•Bromination of phenol occurred and Br-DBPs were formed in PMS oxidation processes.•Brominated phenols were detected as the intermediates.•Br-DBPs could be degraded by excessive SO4−SO4−.•Br− was ultimately transformed to BrO3−BrO3− in the presence of SO4−SO4−.

Formation of halogenated disinfection by-products (DBPs) in sulfate radical (SO4−)(SO4−) based oxidation processes attracted considerable attention recently. However, the underlying reaction pathways have not been well explored. This study focused on the transformation of Br− in cobalt activated peroxymonosulfate (Co2+/PMS) oxidation process. Phenol was added as a model compound to mimic the reactivity of natural organic matter (NOM). It was revealed that Br− was efficiently transformed to reactive bromine species (RBS) including free bromine and bromine radicals (Br, Br2−Br2−, etc.) in Co2+/PMS system. SO4−SO4− played a principal role during this process. RBS thus generated resulted in the bromination of phenol and formation brominated DBPs (Br-DBPs) including bromoform and bromoacetic acids, during which brominated phenols were detected as the intermediates. Br-DBPs were further degraded by excessive SO4−SO4− and transformed to bromate ultimately. Free bromine was also formed in the absence of Co2+, suggesting Br− could be oxidized by PMS per se  . Free bromine was incorporated to phenol sequentially leading to Br-DBPs as well. However, Br-DBPs could not be further transformed in the absence of SO4−SO4−. This is the first study that elucidated the comprehensive transformation map of Br− in PMS oxidation systems, which should be taken into consideration when PMS was applied to eliminate contamination in real practice.

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